The present invention relates to a method for manufacturing a roller which is used in printers, copy machines, etc.
In printers, copy machines, etc., various types of rollers such as charging rollers, developing rollers, transfer rollers, fusing rollers, pressure rollers, etc., are used.
An explanation about a charging roller will be given below for a typical example of such rollers.
Non-contact methods utilizing corona charging, individual charging, needle electrodes, etc., and contact methods utilizing rollers, conductive brushes, etc., are charging methods used for printers and copy machines known in the art. Recently, the method utilizing rollers is most commonly used, since it has various technical advantages; for example, the method is ozone-free.
A semi-conductive roller used in this method is required to have the following features.
(1) no contamination of photosensitive drums
(2) high surface smoothness
(3) stable resistance (semiconductive area)
(4) low eccentricity
(5) low abrasion and high toner resistance
(6) high flexibility
(7) low price
In order to satisfy the above-described features, a semi-conductive roller having a construction as shown in FIG. 2 has been suggested.
This semi-conductive roller has such a construction wherein a core bar is covered by three layers: layer A, which is a flexible foamed layer of EPDM, urethane, etc., and which has a resistance of 1.0 E+04 to 1.0 E+08 xcexa9cm; layer B, which is an elastomer layer having a resistance of 1.0 E+08 to 1.0 E+12 xcexa9cm; and layer C, which is a protection layer formed of a resin such as nylon, etc.
In the above-described construction, it is extremely difficult to form layers having a smooth surface and low eccentricity around the core bar. Of the three layers, it is especially difficult to form the foamed layer having a smooth surface and low eccentricity. Accordingly, a cumbersome method, as disclosed in Japanese Unexamined Patent Application Publication No. 8-22209, is applied, in which, after the foamed layer is formed, the surface thereof is smoothed by polishing and the eccentricity thereof is corrected.
An object of the present invention is to provide a method for manufacturing a roller having high surface smoothness and low eccentricity without performing cumbersome processes such as polishing a foamed layer. According to the present invention, a compound for foaming a foamed (hereinafter xe2x80x9cfoamed-layer compoundxe2x80x9d) is injected into a space between a core bar, which is disposed at the center of a cylindrical mold, and an electron-beam-irradiated tube, which has an outer diameter somewhat smaller than the inside diameter of the cylindrical mold, and which is set inside the cylindrical mold. Then, the foam-layer compound is heated and foamed so that the outer surface of the electron-beam-irradiated tube is pressed against the inner surface of the cylindrical mold.